Controlling the Secondary Flow in a Turbine Cascade by 3D Airfoil Design and Endwall Contouring

Abstract

A highly loaded turbine cascade has been redesigned with the objective to reduce the secondary flow by applying endwall contouring and 3D airfoil design in the endwall regions. The overall loading and the axial area ratio of the cascade have been kept constant. With the tools of a 3D design environment a systematic study has been carried out regarding several features of the endwall pressure distribution and their influence on the secondary flow. Two optimized configurations have been investigated in a high speed cascade wind tunnel. The flow field traverses showed improvements concerning the radial extent of the secondary flow and a decrease in secondary loss of 26 per cent. Unfortunately this reduction was counterbalanced by increased profile losses and higher inlet losses due to increased blockage. The striking feature of the cascade with endwall contouring and 3D airfoil design was a significant reduction of the exit flow angle deviations connected with the secondary flow. The predictions obtained by the 3D Navier-Stokes solver TRACE_S showed a remarkable agreement with the experimental results.

Pressure Surface Separations in Low-Pressure Turbines—Part 2: Interactions With the Secondary Flow

“…The considerable extent of laminar flow on low pressure turbine blades therefore necessitates the use of realistic transition modeling if reasonable predictions of profile loss, and hence efficiency, are sought. Figure 4 shows that the structure of the secondary flow at 125%C X is the same as that reported in other studies of low pressure turbine blades in linear cascade [2,3,10,11]. Furthermore, Figure 3 and Figure 4 show that there is considerable variation in stagnation pressure loss and exit yaw angle in the secondary flow region (from approximately 0% to 20% span).…”

“…Specifying transition at the leading edge on the suction surface resulted in profile losses of approximately 0.04. Other studies of turbine profiles that compared numerical predictions with experiments showed similar behavior [10,11]. Specifying transition at the leading edge on the suction surface is clearly physically unrealistic as the acceleration from the leading edge to peak suction on low pressure turbine blades should keep the boundary layer laminar [12].…”

“…A number of investigators have found that the overall development of the secondary flow in a turbine is particularly sensitive to the flow around the intersection of the foreblade and the endwall [11,14]. This can be explained using simple dynamics.…”

Measurements and modeling of the flow and heat transfer in a contoured vane-endwall passage

“…Duden et al [8] applied axisymmetric profiling to an endwall and found that the extent of the secondary flow was reduced as well as the secondary-flow losses. In two companion works, Harvey et al [11] and Hartland et al [12] have presented the design and experimental validation of a passage subject to nonaxisymmetric endwall profiling.…”

“…Strategies to overcome the aerodynamic losses arising from secondary flows have included the use of endwall profiling and/or secondary air injection to alter the underlying vortical flow within a passage e.g., see [8][9][10][11][12]. Duden et al [8] applied axisymmetric profiling to an endwall and found that the extent of the secondary flow was reduced as well as the secondary-flow losses.…”